I have to say I bought the Draper branded tester because Draper usually produce decent equipment.
This is the same cheap tester available elsewhere on Amazon except it comes with a really tacky (in both senses of the word - the Draper logo feels like a layer of wet PVA glue and sticks to everything).
The machine itself does the job (when you have found a PP3 battery) but I am not sure how long it will last as the case appears to be coming apart from new. The testing is pretty basic - it just tells you whether the 8 wires are connected straight though - not sure if it can test crossover wiring (shouldn't think so as there are no options to choose from).
The instruction book is a disgrace - no real instructions and it doesn't even mention the device model supplied at all. Additionally Draper have removed the model number so there wouldn't be a way to identify the device anyway because the instructions only uses model numbers.
Amazon reckon the list price is over £20. £4 seems about right but don't expect it to last and if you need to use it for work, or on a more than one off basis, forget it - splash out on something that does more and will last.
Update 25/03/12: Returned this item to Amazon for a refund as connectors proving intermittent. Bought a much more expensive and solid built tester by Vitek for £60 that will last for years (not on Amazon - try Misco product code 45773) which is very solidly built, comes with a good quality case, decent instructions and can test R45, R11 (including straight through and crossover arrangements), USB A/B cables and also coax termination.